The field of the disclosure relates generally to ion mobility spectrometer (IMS) systems and, more particularly, to an ionization chamber having a potential-well for ion trapping and ion compression.
At least other some known spectrometry detection devices include ion mobility spectrometer (IMS), such as, for example, an ion trap mobility spectrometer (ITMS). Many of the known ITMS detection systems include a collection device that collects particulate, liquid, and/or gaseous samples from an object of interest. The samples are channeled to an ionization chamber that includes an ionizing source that ionizes the sample to form positive ions, negative ions, and free electrons. The ionization chamber in ITMS detection systems is typically a field-free region. As the ions are generated in the ionization chamber to increase the ion population therein, a retaining grid, or gate, is maintained at a slightly greater potential than the electric field in the ionization chamber to induce a retention field and reduce the potential for ion leakage from the chamber. Thus, the ions are “trapped” within the ionization chamber or ionization region. An electric field is then induced across the ionization chamber and, depending on the polarity of the induced electric field, the positive ions or the negative ions are pulsed from the ionization chamber, through a high-voltage “kickout pulse,” into a drift region through the retaining grid. The ions of the opposite polarity are attracted to the walls of the ionization chamber and are discharged there.
In some ITMS detection systems, the drift region includes a plurality of sequential, annular electrodes. A collector electrode is positioned on the opposite side of the drift region from the ionization chamber and is held at a ground potential. For those systems that use negative ions, the annular electrodes are energized to voltages that are sequentially less negative between the ionization chamber and the collector electrode, thereby inducing a constant positive field. Motion is induced in the negative ions from the initial pulse in the ionization chamber and the ions are channeled through the drift region to the collector electrode. Signals representative of the ion population at the collector electrode are generated and transmitted to an analysis system to determine the constituents in the collected samples.
The population of ions is pulsed into the drift region from the ionization chamber typically in the form of an ion disk with a predetermined axial width value and possibly a trailing ion tail. As the disk of ions traverses the drift region, high-mobility analytes separate from low-mobility analytes induces expansion and distortion of the ion disk. The high-mobility analytes form a disk that transits faster than a disk formed of low-mobility analytes and the disks may overlap as they are received at the collector electrode. The peaks on the trace thus generated on the spectral analysis equipment are distorted with poor resolution and are difficult to analyze. Moreover, in many ITMS detection systems, there is no precise control over the width of the ion disk injected into the drift region. Fundamentally, this is due to inconsistent, and sometimes, incomplete clearing out of the ionization chamber due to non-homogeneity of the electric field induced in the ionization chamber, e.g., low field regions at the back of the ionization chamber.